Sheets of a first material with particles of a second material embedded within them are used for various purposes. Such particles may cause a change in certain properties of the sheet such as strength, brittleness, heat resistance, etc. that are beneficial for various purposes. Sheets with particles are also used for optical purposes. For example, a transparent sheet may have particles of a different refractive index embedded in it. The transparent sheet acts as a light guide, and the embedded particles disperse the guided light. This apparatus can be used as a light source. The particles may be dyes added to impart color to the sheet. Sheets with a constant concentration of particles are used where the concentration of particles is not a constant, but varies throughout the sheet.
One use of a sheet with a varying concentration of particles is for a light source with a particular light emanation pattern. Various light emanation patterns can be achieved by employing various concentration profiles of the particles. The particle concentration along the sheet can be adjusted to provide a uniform extraction of light from the sheet, or light extraction in any required pattern. Such light sources find many uses in the art, including as backlights for LCD displays, as light sources of photography and as architectural light sources. Sheets with varying concentration of particles are also used for artistic purposes, and for road signs, material sciences, and optics.